BTK and B-cell chronic lymphocytic leukemia: Ibrutinib, a selective Bruton tyrosine kinase (BTK) inhibitor initially approved by the FDA in 2013 for treating chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL), has emerged as a potential antiviral candidate based on a high-throughput screening for its efficacy against vaccinia virus (VACV).